1. Field of the Invention
This invention relates to diamond studded insert drag bits.
More particularly, this invention relates to drag bits with a multiplicity of individual diamond faced tungsten carbide inserts mounted in the face of the drag bit with wear pads forming hydraulic passages on adjacent sides of the face of the drag bit to direct hydraulic fluid over the inserts to cool and clean the diamond faced insert blanks.
2. Description of the Prior Art
Most state of the art diamond drag bits are designed with the first consideration given to location of the individual diamond cutter inserts.
For example, U.S. Pat. No. 4,098,363 discloses a diamond drill bit employing spaced, shaped diamond cutter elements arranged in rows separated by large fluid channels. The channels are formed in the bit body and are utilized for bit cleaning and detritus removal action. A series of nozzles are randomly placed within the channels. The channels themselves distribute the fluid or drilling mud over the array of diamond cutters. This type of bit is normally fabricated from a material which is highly resistant to erosion, especially where fluid channels are provided in the face of the bit. The diamond drill bit just described is cast from expensive carbide material with the waterway channels formed therein to provide an erosion resistant face for the bit body.
This patent is disadvantaged in that the cutting face of the bit is directly exposed to the hole bottom. In other words, as the bit rotates the cutting edge of the diamond inserts come in full contact with the hole bottom and are subjected to a rapid wear rate and insert breakage. Since the diamond inserts are fully exposed to the hole bottom, the inserts, as well as the supporting structure, would necessarily have to be fabricated from a highly wear resistant material.
In drag bit designs utilizing diamond bit hydraulic theories, the cleaning action is very good. Unfortunately, as the diamond drag cutter wears, the bit body "bottoms-out" and insufficient weight is applied to the drag cutters. Diamond bits typically have bottom hole standoffs of 0.100" while the diamond drag cutter stands some 0.500". To fully utilize the potential economic life of the diamond drag cutter, it must be kept in engagement with the rock and kept clean through all phrases of the drilling operation. The hydraulic design needs to vary with cutter wear to maintain cleaning.
The diamond studded insert and drag bit of the present invention protect the insert studs which are inserted within the face of the drag bit. The basic material of the drag bit need not be highly wear resistant since the face of the bit is not directly exposed to the hole bottom. By utilizing one or more wear pads on the face of the drag bit to form fluid passages to direct fluid over the diamond inserts, the wear pad easily conforms to the hole bottom and protects the majority of the diamond inserts in the channels formed by the wear pad on the face of the drag bit. As the tips of the diamond inserts contact the hole bottom, the wear pads conform to the hole bottom thereby forming a seal between the hole bottom and the bit to direct hydraulic mud through the channels and over the diamond tipped cutters. As the diamond tips wear down the wear pad is equally worn so that a constant drag bit penetration rate is maintained. The best economic use of the drag cutters is made when good hydraulics are maintained throughout the cutter life. The wear pads limit penetration of each of the individual diamond cutters, thus protecting the inserts from breakage that could occur if the inserts embed themselves too deeply in the borehole bottom.
The wear pads may be fabricated from a variety of relatively soft materials ranging from assorted plastics to aluminum, copper, bronze or mild steel depending upon the rock bit formations in which the drag bit is utilized.